1. Technical field
The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium useful for a magnetic card or the like used in settlement of accounts in bankings, circulations, transportations, or telecommunications. Also, the present invention provides a process for producing such magnetic recording medium.
2. Prior art
In recent years, magnetic recording media such as magnetic cards have been widely adopted as means for settlement of accounts in the fields of bankings, circulations, transportations or telecommunications. However, the magnetic cards are exposed to risks of illegal or unauthorized uses such as forgery or modification. Accordingly, magnetic recording media having high confidentiality are required, especially with machines for settlement of accounts.
As means for enhancing the confidentiality of magnetic recording medium, it was proposed to write a fixed or permanent signal for identifying the magnetic recording medium, which is difficult to rewrite, on an area different from the area for ordinary signal recording-reproduction.
More particularly, Japanese Patent Kokoku No. 49-37529 (1974) proposed to provide a fixed identifying pattern by varying alternately the direction of the axis of easy magnetization of acicular magnetic particles in the magnetic layer with respect to the direction of reading; Japanese Patent Kokai No. 50-79311 (1975) proposed to provide a fixed identifying pattern by applying a magnetic coating on an ordinary magnetic layer on which an identifying information has been recorded, so that magnetic particles dispersed in the magnetic coating are oriented under the influence of the magnetic field from the recorded information and the directions of the orientation of them are physically fixed; and Japanese Patent Kokai No. 5-318974 (1993) proposed to provide an identification pattern on a magnetic layer containing magnetic particles having a coercive force of more than 4,500 Oe dispersed in a binder, by magnetically transferring an identification information recorded on an ordinary magnetic recording medium to another magnetic layer coated on the ordinary magnetic recording medium by the magnetic field from the recorded identification information. It is difficult to modify these identification patterns if ordinary magnetic recording and reproducing head are used.
However, the method of providing a fixed identifying pattern by varying alternately the direction of the axis of easy magnetization of acicular magnetic particles in the magnetic layer with respect to the direction of reading disclosed in Japanese Patent Kokoku No.49-37529 not only necessitates a special orientation apparatus in producing the magnetic recording medium, thereby increasing the cost for production and machinery cost.
On the other hand, with respect to the method of providing a fixed identifying pattern by applying a magnetic coating on an ordinary magnetic layer on which an identifying information has been recorded so as to transfer the recorded information from the ordinary magnetic recording layer to the magnetic coating, the method disclosed in Japanese Patent Kokai No. 50-79311 has a drawback that the output from the identification pattern is low.
This drawback has been unexpectedly overcome according to the present invention which uses magnetic orientation which, however, is considered to exert an adverse effect on the magnetic transfer system disclosed in this reference.
Further, the magnetic transfer method disclosed in Japanese Patent Kokai No.5-318974 has a deficiency in that there is a high risk of modification or forging of the magnetic recording medium because it is well know in the art that if a magnetic recording and reproducing head utilizing a magnetic core having saturation magnetization of 22 kilo gauss or more is used it is quite possible to rewrite information on a magnetic recording medium having a high coercive force up to about 8,000 Oe. Moreover, in the magnetic recording medium of this reference, the magnetic layer of a higher coercive force than the ordinary magnetic layer of lower coercive force is on the side closer to the magnetic head and accordingly is exposed to a stronger magnetic field. Accordingly, there is a high risk of modification or forging as it is relatively easy to rewrite the identification information inherent to the magnetic recording medium. With this system, it is not only difficult to transfer the identification information signal to the magnetic layer containing magnetic particles having a coercive force of 4,500 Oe or more due to this high coercive force but also difficult to read the recorded information due to the low saturation magnetization.
The present inventors have found that this problem is overcome by using magnetic particles having a relatively low coercive force.